The invention relates to a drive system for escalators or moving walkways, comprising at least one drive motor, which optionally cooperates with a gear, at least one drive chain, which is configured as a plate link chain, reversing elements for the drive chain as well as means for minimising the polygon effect, which occurs during the entry and the reversing of the chain.
In the reversing of the chains of pedestrian conveyor systems, in particular escalators and moving walkways, by means of a chain wheel, polygon and revolution effects occur which in particular adversely affect the quiet running of the escalator or moving walkway.
The polygon effect is caused by the polygonal rest of the chain on the chain wheel. With increasing rotation angle, the effective radius of the chain wheel varies, whereby the velocity of the chain oscillates between a maximum and a minimum value. When engaging the chain wheel, the chain rolls and the teeth of the chain wheel have different velocities, which cause impacts. The revolution effect is caused by the angular momentum which is transmitted from the chain wheel onto the chain links and thus onto the steps or pallets. After the chain has run out of the chain wheel, this angular momentum is temporarily maintained due to the inertia of the system, which leads to the so called curling of the chain. The angular momentum is reduced by friction in the chain respectively by impacts between chain and guiding if a chain guiding element is provided.
In a usual arrangement, where the chain wheel drive also reverses the chain, the chain is tangentially supplied to the chain wheel. Thereby, the chain wheel and the chain have different speeds upon engagement of the chain wheel. Impacts between the chain and the chain wheel are caused in the direction of the chain strand, which, in practice, can be measured as accelerations of the respective transport elements, such as for example the steps or pallets of escalators or moving walkways. Besides the generated noise, these periodically occurring impacts lead to high stresses of the chain, the chain wheel and the drive.
European Patent document EP-A 0 711 725 describes a device for guiding a band continuum of escalators or moving walkways, in which the chain rolls are guided by means of a supporting rail having a running path and by means of an equalizing rail having a running path. At the entry of a chain wheel, which reverses the band continuum, the chain rolls are guided from the linear running path of the supporting rail onto the curved running path of the equalizing rail and from there towards a tangent point into engagement with the chain wheel.
From the running path of the supporting rail to the tangent point, the chain rolls are guided into a direction orthogonal to the running direction, over a distance which is transverse to the running direction, towards the chain wheel, which is intended to have an advantageous effect on the quiet running of the band continuum. This special curve shape of the connection element furthermore is intended to help to reduce the polygon effect.
The German magazine Klepzig Fachberichte 79 (1971), H 8, M 200, pages 437 through 439, discloses movement problems of chain drives having large chain links. The article discusses consequences of the polygon effect, wherein a number of possible solution in the mechanical field are proposed. Among other things, the reversing of a chain by means of a chain starwheel with equalizing gear is proposed, wherein the chain stud maintains its horizontal displacement and velocity as long as the next roll engages, so that a complete chain link has entered the chain starwheel. Only then, is the chain link reversed.
Both of the foregoing publications describe quite extensive mechanical constructions for reducing the consequences of the polygon effect in the reversing of the chain over a reversing wheel.
It has been proposed to use plate link chains for the step or pallet band which have a greater pitch depending on the step or pallet width, for example approximately 200 or approximately 400 mm, for the purpose of optimization of the drive concep. However, it is possible that these desired greater chain pitches will cause problems with respect to the polygon effect during the reversing and possibly with respect to the synchronous drive of the handrail.
Furthermore, escalators and moving walkways are generally known for indoor use, for example in department stores or the like in which, with regard to relatively low forces, the step or pallet studs including the rollers, which cooperate with the steps or pallets, are positioned in the respective joint areas of the drive chains. However, during the reversing of the drive chains, the existing polygon effect still causes problems.
German Utility Model 18 92 806 discloses an escalator comprising circulating, endless chain bands, which are held together by individual chain links, while steps, which are hung up in step axes, are interposed. The link plates of individual chain links, which connect the chain rolls to each other, serve as a connection of the front step axes. The distance between adjacent step axes corresponds to the pitch of the steps and is a multiple of the pitch of the chain band. Three chain links for each step are represented.
German Utility Model 74 29 118 describes an improved chain drive, in particular for escalators, in which each step has at least one end articulated at a chain, joint. The chain essentially comprises a number of joints, which corresponds to the number of steps. In order to assure a correct, essentially tangential entry and exit of the chain into and out of the chain wheel, the chain is guided over at least a part of the reversing distance thereof. If only one joint is used for each step, at least two joints shall always be in engagement with each chain wheel for avoiding polygon effects.